It is the purpose of this study to resolve the cold resistant nature of the brain of a mammalian hibernator. The topics of interest and investigation are: (1) Fatty acid metabolism, primarily that associated with the desaturation of fatty acids, (2) glycerophospholipid metabolism, (3) membrane lipid turnover, and (4) membrane biogenesis. The use of the hibernating species of mammal, the hamster, is employed in these studies since it can alter naturally when cold exposed, both the chemical and physical nature of its neural elements.